Uterine Lavage
Post partum mares usually come into heat around nine days after foaling. However, the conception rate of mares bred at this time is low, typically in the 35-55% range. The conception rates of mares coming into heat for the second or third times, approximately eighteen or twenty seven days after foaling, respectively, is generally higher, though this requires the mare to be bred again, at added expense, and also leads to a loss in the mare's productivity. This low initial conception rate may be related to a number of factors, including retained placenta or metritis (infection) in the uterus, as well as poor involution post foaling, excessive lochia and low grade endometritis as a result of both physiological and confinement management practises.
In an effort to decrease levels of infection, practitioners have often treated mares with antibiotics following foaling. However, this is expensive, and the wide spread use of antibiotics in such circumstances is discouraged as it tends to increase levels of antibiotic resistance. This approach also ignores subinvolution, one of the main problems encountered with post partum mares.
Flushing of the uterus with sterile fluid, possibly containing antibiotics, has also been used to clear the uterus of retained placenta and reduce levels of infection. The flushing is achieved by use of gravity to feed lavage fluid from a funnel through a flexible tube into the uterus. The fluid drains by siphon effect through a second tube leading from the uterus, or through the same tube, after the lavage fluid has been passed into the uterus. This method is fairly well known among practitioners, but requires the presence of two people, one to locate the tubes and the other to dispense the fluids, and is also time consuming and awkward. It is also difficult to control the rate of flow of lavage fluid into the uterus, and it is not possible to sterilize the apparatus. Further, it is desirable to use hot water to carry out the lavage, and this requires water to be heated and then transported to the lavage site. Understandably, in these circumstances, control of the temperature of the water is difficult. Understandably, the amount of work and organization required to carry out such a flushing operation precludes its use except in the most severe or valuable of cases.
Uterine flushing is also utilized in the collection of embryos (fertilized ova) from animals, as in for example Canadian Patent No. 1,073,286, issued on Mar. 11, 1980, to the Milk Marketing Board, which discloses "Apparatus For Use In Collecting Eggs from Animals". The apparatus includes a flexible, small diameter catheter for insertion into the vagina of an animal and through the cervix, the insertion assisted by use of an outer plastic sheath and a rigid tubular member. The catheter is located in the cervix with an inflatable cuff anterior to the cervix and defines a plurality of lumens, one an air passage for the inflatable collar, one for supplying fluid, and the remaining one acting as a drain. In use, the end of the catheter, and also the end of the supply lumen, is located well into one of the uterine horns. Fluid is supplied using a syringe, typically of 60 ml capacity, operated by an assistant, through the supply lumen into the uterine horn and withdrawn anterior to the inflated cuff, through the inlet to the drain lumen, into a second syringe. The collected fluid is then examined for the presence of an embryo.
The catheter is suitable for use only in the bovine and the form of the catheter makes it difficult to flush the uterus effectively, as the end of the catheter is located in one of the two horns of the uterus, and the other horn will not be efficiently flushed. As the catheter has little inherent rigidity it would likely be difficult to manipulate so as to reposition the end of the catheter in the other uterine horn. The insertion of the catheter also requires use of an outer plastic sheath and a rigid member, adding to the cost of the equipment and making sterilization more difficult. The very small diameter limits the flow of fluid for flushing, for example it would take approximately 45 minutes to supply one liter of fluid. The small diameter also limits the size of the drain lumen such that it plugs easily and will not provide a siphon effect for draining fluid from the uterus, such that some form of suction must be provided or the drain. In practice, the catheter is rarely used, even by bovine embryo transfer specialists.